Moving vehicles such as automobiles, trucks, aircraft, missiles, ships and rail vehicles carry components that require protection against severe shock from impact caused by rough terrain or other disturbances as the case may require. Such components include vehicle electronics, motors, fans, machinery, transformers, shipping containers, railroad equipment, pumps, numerical control equipment and aircraft/missile electronics. Generally such protection is provided by a vibration isolator or a similar component.
One function of a vibration isolator is to provide a means whereby a component is protected against handling impact loads being transmitted from a base or frame of a vehicle such as an aircraft on which the component may be mounted. Protection against such loads is usually accomplished by storing energy within a resilient medium and then releasing such energy at a relatively slower rate. Generally, such isolators comprise a rubber member which, together with the mass of the mechanism which it supports, has a natural frequency that is sufficiently lower from that of the disturbing force so as to bring about a minimum transient response of the supported mechanism, and yet have sufficient static load-carrying capacity to support the load of such mechanism. Correct matching of a vibration isolator to specific application is essential; for example, a given vibration isolator may be effective in a case where the mechanism is to be subjected to a relatively high magnitude of loading within a short time interval and yet may tend to magnify the shock where the mechanism is to be subjected to a loading of considerably smaller magnitude but with a longer time interval.
As used herein, the term "vibration" is used to describe a continuing periodic change in the magnitude of a displacement with respect to a specified central reference point. Also, as used herein, the term "mechanical vibration" is used to describe the continuing periodic motion of a solid body at any frequency. In most cases, mechanical vibration may be isolated by placing a resilient medium between the source of vibration and a protected unit to reduce the magnitude of the force transmitted from a structure to its support or, alternatively, to reduce the magnitude of motion transmitted from a vibrating support to the structure. One of the prime considerations in the isolation of vibration is the proper use of a vibration isolator under various load configurations with respect to the loading of such vibration isolator, the desired natural frequency, the position and location of the vibration isolator and the relationship of the structural response of equipment to which such isolator is attached.
It can be shown that for a vibration isolator to be effective, the natural frequency thereof should be less than 40% of the frequency of the disturbing source. Those skilled in the art will recognize that the natural frequency is the frequency at which a freely vibrating mass system will oscillate once it has been disturbed. There are many instances where equipment must operate over a fairly wide frequency range, for example, as in aircraft where vibrations may occur in the range from 5 to in excess of 2000 Hertz. In many instances, the equipment will thus be subjected to lower frequencies initially; will pass through a condition known as resonance or resonant frequency; and may be designed for normal operation at a frequency which is considerably higher than the resonant frequency. As used herein, resonance exists when the natural frequency of a mass support on a vibration isolator coincides with the frequency of the disturbing vibratory forces; and resonant frequency means that frequency at which such coincidence occurs.
A condition of resonance causes magnification of the disturbing vibratory forces and may be harmful, and sometimes destructive, to equipment subjected to such forces unless proper controls can be effected. To provide such controls, the resilient medium of a vibration support must be provided with suitable damping. While vibration damping is helpful under conditions of resonance, it may be detrimental in some instances to a system at frequencies above the resonant frequency.
A stated factor that must be considered in the selection of a vibration isolator is its configuration and the type of loads it will be required to support. In particular, the loads may be in compression, shear or tension direction or combinations thereof. For example in a vibration isolator having a configuration with elastomer bonded between two rigid plates, the mounted component exerts only a static gravitational downward force onto the support. Such a vibration isolator will mostly experience a load support in compression with some combination of induced shear loads. If the vibration isolators are installed above the supported protected components, then each vibration isolator will mostly experience a tension load with some induced shear loading. If the vibration isolators are mounted to the side of the supported protected components, each vibration isolator will mostly experience a load supported in shear with possible compression and tension load.
However, in many applications the vibration isolators will experience all the modes of loading or combinations thereof. In particular, the vibration isolator will not only have to support the protected component, but will also have to hold it to the structure wherein the vibration isolator is in tension or help the protected component from shifting wherein the vibration isolator is in shear. This invention is directed to the case wherein various types of loads including compression, shear or tension modes or combinations are incurred by the vibration isolator. Furthermore, it would be advantageous to have one mount design that could simultaneously accommodate all modes of loads.